Selective oxidation of alkenes using [bmim]5[PW 11ZnO39]·3H2O hybrid catalyst

Article abstract of DOI:10.1007/s13738-012-0212-2

The catalytic activity of [bmim]₅[PW₁₁ZnO ₃₉]·3H₂O as a hybrid catalyst was studied in the oxidation of various alkenes in acetonitrile, using hydrogen peroxide as oxygen source. The effect of reaction parameters such as type of solvent and oxidant, amount of catalyst and oxidant, and temperature was also investigated. From our results, [bmim]₅[PW₁₁ZnO₃₉]·3H ₂O hybrid catalyst gave higher yields and selectivity in the oxidation of alkenes and was reused four times without loss of its catalytic activity.

Full text of DOI:10.1007/s13738-012-0212-2

J IRAN CHEM SOC (2013) 10:777–782
DOI 10.1007/s13738-012-0212-2
ORIGINAL PAPER
Selective oxidation of alkenes using [bmim]5[PW11ZnO39]Á3H2O
hybrid catalyst
•
Zahra Nadealian Valliolah Mirkhani Bahram Yadollahi Majid Moghadam
•
•
•
•
Shahram Tangestaninejad Iraj Mohammadpoor-Baltork
Received: 6 July 2012 / Accepted: 27 December 2012 / Published online: 16 April 2013
Ó Iranian Chemical Society 2013
Abstract The catalytic activity of [bmim]5[PW11Z-
nO39]Á3H2O as a hybrid catalyst was studied in the oxi-
dation of various alkenes in acetonitrile, using hydrogen
peroxide as oxygen source. The effect of reaction param-
eters such as type of solvent and oxidant, amount of cat-
alyst and oxidant, and temperature was also investigated.
From our results, [bmim]5[PW11ZnO39]Á3H2O hybrid cat-
alyst gave higher yields and selectivity in the oxidation of
alkenes and was reused four times without loss of its cat-
alytic activity.
are technically vital products that obtained from the reac-
tion of epoxides [4]. Indeed, pesticides, rubber promoters,
chiral pharmaceuticals, and peroxy paints are produced
from organic intermediates such as cyclooctene and
cyclohexene oxides [5]. For this purpose, chemists have
been used different homogenous and heterogeneous cata-
lysts [6–8] and various oxidants such as PhIO, NaC1O,
percarboxylic acids, molecular oxygen, and hydroperox-
ides [9–12]. Among these oxygen donors, the greener
oxidants (O2 and H2O2) are cheap, clean, and environ-
mentally benign ones [13–18].
Keywords Hybrid catalyst Á Polyoxometalate Á Oxidation Á
Ionic liquid Á Alkenes
Polyoxometalates as a unique class of inorganic metal–
oxygen clusters bear many properties that make them
attractive for applications in catalysis [19], electrochemis-
try [20], magnetism [21], optics [22], and medicine [23].
The catalytic activity of polyoxometalates has attracted
much attention because their acidic and redox properties
can be controlled by transition metal substitution and
changing the type of the counter-cation [24–26]. The
technologically significant aspect of polyoxometalates in
catalysis is their specific stability toward oxygen donors
such as O2 and H2O2. Therefore, various structures of
polyoxometalates are useful for liquid phase oxidation of
different organic substrates with hydrogen peroxide [27].
Ionic liquids (IL) have unique properties such as low
melting point, negligible vapor pressure, high ionic con-
ductivity and wide electrochemical stability [28]. These
compounds are used in many fields including hybrid
compounds synthesis, organic chemistry, electrochemistry,
catalysis, physical chemistry, and engineering [29, 30].
The design, synthesis, characterization, and application
of novel hybrid materials have established new area of
research in chemistry and material science in order to
obtain multifunctional structures with special property
including catalytic, electronic, and optical properties [31,
Introduction
Selective and efficient oxidation of hydrocarbons to useful
corresponding organic compounds has received much
attention in recent years. The conversion of raw materials
like alkenes into industrial chemicals is one of the impor-
tant applications of epoxidation reactions [1–3]. Deter-
gents, surfactants, antistatic agents and corrosion
protection agents, lubricating oils, textiles, and cosmetics
Z. Nadealian Á V. Mirkhani (&) Á B. Yadollahi (&) Á
M. Moghadam (&) Á S. Tangestaninejad Á
I. Mohammadpoor-Baltork
Department of Chemistry, University of Isfahan,
81746-73441 Isfahan, Iran
e-mail: Mirkhani@sci.ui.ac.ir
B. Yadollahi
e-mail: yadollahi@chem.ui.ac.ir
M. Moghadam
e-mail: moghadamm@sci.ui.ac.ir
123

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J IRAN CHEM SOC (2013) 10:777–782
32]. In recent years, there have been an abiding research
interest in synthesis of hybrid catalysts with polyoxo-
metalates and room temperature ionic liquids due to their
extensive applications in various fields such as catalysis,
bio catalysis, thermally stable lubricants, hybrid inorganic–
organic nanocompositse, electrochemistry, and photo-
chemistry [33–35].
reaction, the reaction mixture was cooled to room tem-
perature; the solvent was evaporated and n-hexane (10 mL)
was added. The catalyst was filtrated and washed with
n-hexane. The solvent was evaporated and the pure product
was obtained by chromatography on a short column of
silica gel.
In continuation of our previous works on the investigation
of catalytic activity of hybrid compounds [36–38], here, we
wish to report the catalytic activity of [bmim]5[PW11Z-
nO39]Á3H2O hybrid compound in the oxidation of alkenes
with hydrogen peroxide (30 %) in acetonitrile as solvent
(Scheme 1). The effect of different parameters such as sol-
vent, oxidant, and temperature on the activity and selectivity
of the catalyst was also studied (Scheme 1).
Results and discussion
The catalytic activity of the prepared catalyst was tested
using cyclooctene as reference alkene. In order to optimize
the amount of [bmim]5[PW11ZnO39]Á3H2O hybrid catalyst,
various amounts of catalyst were used for oxidation of
cyclooctene. As shown in Fig. 1, the epoxide yield was
100 % in the presence of 0.05 mmol of hybrid catalyst
under reflux conditions after 1 h.
Experimental
For choosing the reaction media, various polar, non,-
polar coordinating, and protic solvents including CH3CN,
CH2Cl2, EtOAc, MeOH, CHCl3, n-C6H12, and H2O/
CH3CN were tested as reaction medium. The higher cata-
lytic activity and solubility of the catalyst and substrate are
the key factors for choosing the acetonitrile as the best
solvent for epoxidation reaction. The results are summa-
rized in Table 1.
General
All materials were commercial reagent grade and obtained
from Merck and Fluka chemical companies. Alkenes were
passed through a column containing active alumina to
remove peroxidic impurities. The [bmim]5[PW11Z-
nO39]Á3H2O (IL-POM(Zn)) hybrid catalyst was synthesized
according to the published procedure [39] and its spectro-
scopic and analytic data are in according with the reported
literature data. The UV–vis spectra were recorded from 200
to 800 nm on a 160 Shimadzu UV–vis spectrophotometer.
FT-IR spectra (400–4,000 cm-1) were recorded as KBr
pallets using a JASCO 6300 spectrophotometer. Gas
chromatography (GC) experiments were performed with a
Shimadzu GC-16A instrument using a 2 m column packed
with silicon DC-200 or Carbowax 20M. Hydration water
contents were determined by thermogravimetric analysis
on a Mettler TA4000 thermobalance instrument.
Then, the effect of different oxidants on the catalytic
activity of [bmim]5[PW11ZnO39]Á3H2O hybrid catalyst was
studied in the epoxidation of cyclooctene. Different oxygen
donors such as NaIO4, Urea-H2O2 (UHP), tert-BuOOH,
and H2O2 were also examined. The results, which are
summarized in Table 2, showed that hydrogen peroxide is
the best oxygen source.
In order to find the optimized amount of hydrogen
peroxide, the oxidation of cyclooctene was carried out
using different amounts of H2O2 (30 %) (0.2, 0.5, 0.8, and
1 ml). As shown in Fig. 2, the higher conversion was
obtained when the reaction was carried out with 1 mL
H2O2 (30 %).
Typical procedure for oxidation of alkenes
with hydrogen peroxide catalyzed by IL-POM
The effect of reaction temperature on the oxidation
of
cyclooctene
with
H2O2
catalyzed
by
All reactions were carried out in a 25-mL glass reactor
equipped with a reflux condenser. In a typical experiment,
alkene (1 mmol), [bmim]5[PW11ZnO39]Á3H2O catalyst
(0.05 mmol), acetonitrile (3 ml), and hydrogen peroxide
(1 ml, 30 %) were mixed and stirred at 353 K. The reac-
tion progress was monitored by GC. At the end of the
n
[
] [PW11Z
bmim 5
].
O39
3H2O
+
Oxidation products
H
N H
/ 2O2
C
3C
O
Scheme 1 Epoxidation of alkenes with H2O2 catalyzed by
[bmim]5[PW11ZnO39]Á3H2O
Fig. 1 The effect of amount of [bmim]5[PW11ZnO39]Á3H2O catalyst
on the epoxidation of cyclooctene after 1 h
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J IRAN CHEM SOC (2013) 10:777–782
779
Table 1 Effect of solvent on the oxidation of cyclooctene catalyzed
by [bmim]5[PW11ZnO39]Á3H2O
Table 3 Effect of temperature on the oxidation of cyclooctene cat-
alyzed by [bmim]5[PW11ZnO39]Á3H2O
Row
Solvent
Conversion (%)a after 1 h
Row
Temperature (°C)
Conversion (%)a after 1 h
1
2
3
4
5
6
7
CH3CN
CH2Cl2
CHCl3
100
27
1
2
3
4
25
5
14
40
10
60
39
H2O/CH3CN
MeOH
51
Reflux
100
38
Reaction conditions: cyclooctene (1 mmol), H2O2 (1 mL), catalyst
(0.05 mmol), CH3CN (3 ml)
n-Hexane
EtOAc
Trace
15
a
GC yield
Reaction conditions: cyclooctene (1 mmol), H2O2 (1 mL), catalyst
(0.05 mmol), solvent (3 ml) under reflux conditions
a
GC yield
substrates were successfully oxidized to their oxidation
products under reflux conditions (Table 4). It is clear that
electron rich olefins are more reactive than electron poor
ones. Also, it was found that the alkenes were not oxidized
in the absence of catalyst or oxidant. In the case of
cyclooctene, the cyclooctene oxide was the sole product
with 100 % yield. Oxidation of cyclooctene in the presence
of ionic liquid was carried out and the result indicated that
ionic liquid alone was almost inactive. On the other hand, it
was observed that the sodium and ammonium salts of
polyoxometalate showed low catalytic activity in this
oxidation reaction. It seems that a synergistic effect
between the ionic liquid and the polyoxometalate due to
nearing the size of two structures increased the catalytic
activity of hybrid catalyst. In the oxidation of 6,6-dimethyl-
2-methylene-bicyclo[3.1.1] heptane, the corresponding
epoxide was produced in 93 % yield and 100 % selectivity.
In the case of limonene, the ratio among 1,2-and 8,9-
epoxides was 6.1.
Table 2 Effect of oxidant type on the oxidation of cyclooctene cat-
alyzed by [bmim]5[PW11ZnO39]Á3H2O
Row
Oxidant
Conversion (%)a after 1 h
1
2
3
4
5
H2O2
100
15
NaIO4
H2O2/Urea (UHP)
tert-BuOOH
No Oxidant
31
49
Trace
Reaction conditions: cyclooctene (1 mmol), oxidant (10 mmol), cat-
alyst (0.05 mmol), CH3CN (3 mL) under reflux condition
a
GC yield
[bmim]5[PW11ZnO39]Á3H2O was also investigated. It was
observed that in the oxidation of cyclooctene with H2O2
catalyzed by [bmim]5[PW11ZnO39]Á3H2O at room tem-
perature, small amounts of oxidation product was detected
in the reaction mixture. While, by increasing the reaction
temperature (reflux conditions), the conversion increased
(Table 3).
Interestingly, in the oxidation of styrene and a-methyl-
styrene, the major products were benzaldehyde and ace-
tophenone, respectively. Oxidation of cyclohexene was
accompanied by allylic oxidation. The notable feature of
the catalytic oxidation with [bmim]5[PW11ZnO39]Á3H2O is
that non-activated terminal olefins such as 1-octene,
1-hexene could be transformed to their corresponding
epoxides in good yields. These results show that the con-
jugation of aromatic ring with carbonyl group stabilizes the
products.
Under the optimized conditions, which obtained for
oxidation of cyclooctene, oxidation of different alkenes
such as cyclohexene, styrene, a-methylstyrene, 1-heptene,
1-octene, and 1-dodecene were investigated. Different
Catalyst reusability
The reusability of the [bmim]5[PW11ZnO39]Á3H2O hybrid
catalyst was examined using cyclooctene as model reac-
tion. For each of the repeated reactions, the solvent was
evaporated and n-hexane (10 mL) was added. The catalyst
was filtrated, washed with n-hexane, dried at 50 °C, and
reused in the next run. The results, Fig. 3, indicate that the
[bmim]5[PW11ZnO39]Á3H2O can be recycled four consec-
utive times without a significant decrease in its activity.
Fig. 2 The effect of oxidant amount on the epoxidation of cyclooc-
tene after 1 h
123

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J IRAN CHEM SOC (2013) 10:777–782
Table 4 Epoxidation of alkenes with H2O2 catalyzed by [bmim]5[PW11ZnO39]Á3H2O
Entry
Substrate
Products
Time
(h)
Conversiona
(%)
Selectivityb
(%)
TOF
(h-1
)
1
1
100
100
20.00
O
2
1
94
(1) 8
(2) 88
(3) 4
18.80
O
OH
O
1
2
3
3
4
3
4
93
98
100
6.20
4.90
O
(1) 86
(2) 14
O
O
1
2
5
6
4
4
91
94
(1) 31
(2) 69
4.55
4.70
O
O
O
2
1
(1) 12
(2) 88
O
1
2
7
8
9
1
74
68
88
100
100
100
14.80
9.07
5.87
O
1.5
3
O
O
Reaction conditions: alkene (1 mmol), H2O2 (1 mL), catalyst (0.05 mmol), CH3CN (3 mL) under reflux conditions
a
GC yield
Reaction mechanism consideration
A proposed reaction mechanism for styrene, as an example,
was given in Scheme 2. In the first step, oxygen transfer
from hydrogen peroxide to a PW11Zn cluster of IL-
POM(ZnII) occurred, leading to a higher valent transition
metal-oxo compound (IL-POM–ZnIII = O). The next step
is the formation of ZnIII-peroxocomplex under the inter-
action with H2O2. Afterward, styrene was bound with one
of the metal-peroxo bonds to produce the peroxometallo-
cycle (the third step). In the fourth step, the peroxometal-
locycle is broken and styrene oxide was produced [40–42];
simultaneously, the H2O2 is consumed, and the ZnIII-complex
Fig. 3 The results of [bmim]5[PW11ZnO39]Á3H2O catalyst recovery
in the oxidation of cyclooctene with hydrogen peroxide
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